Speaker
Description
As the lensing signal increases near massive foreground clusters, higher-order effects become increasingly important, requiring an accurate treatment of the lens equation beyond the first-order approximation. While conventional galaxy shape estimators have been extensively studied in the perturbative regime of weak lensing, recovering large shear signals and higher-order distortions under realistic observing conditions remains challenging due to the presence of point spread functions (PSFs), noise, and intrinsic galaxy morphology variations. In particular, flexion, which describes the second-order distortion of galaxy images, provides valuable information about small-scale mass structures such as cluster subhaloes, but is difficult to measure because of its intrinsically weak signal and contamination from shape noise and shear.
In this work, we develop improved methods for measuring gravitational shear and flexion in the environment of the massive galaxy cluster Abell 2744. For shear measurement, we introduce a non-perturbative approach capable of accurately recovering large shear signals (\gtrsim 0.5) under general observing conditions, including realistic PSF effects and noise. For flexion measurement, we develop a new estimator based on the gradient analysis of galaxy surface brightness, extending the theoretical framework to capture higher-order lensing distortions. The performance of these methods is validated using extensive simulations covering diverse PSF models, galaxy morphologies, and signal-to-noise ratios.
Applying these techniques to JWST observations of Abell 2744, we aim to construct reliable shear and flexion maps around the cluster, enabling more precise reconstruction of the underlying dark matter distribution and providing constraints on small-scale structures such as galaxy cluster subhaloes.